Bistable electromagnetic actuator

ABSTRACT

A bistable electromagnetic actuator has an armature maintained in one stable position magnetically, by means of a permanent magnet, and in a second stable position by means of a spring. Either position may be assumed by energization of a coil with current of the appropriate polarity or by application of mechanical force. A magnetic shunt maintains flux through the permanent magnet during energization of the coil.

United States Patent [191 Read, Jr.

Aug. 28, 1973 IISTABLE ELECTROMAGNETIC ACTUATOR [75] lnventor: Reginald A. Read, Jr., La Grange, Ill.

[73] Assignee: Regdon Corporation, Brookfield, lll.

[22]v Filed: Jan. 18, 1972 [21] Appl. No.: 218,770

[52] US. Cl 335/229, 335/234, 335/236 [51] Int. Cl. 1101f 7/08 [58] Field of Search 335/229, 230, 234,

[56] References Cited UNITED STATES PATENTS 12/1959 Troy 335/299 X 2/1962 Chase 335/229 X 6/1962 Conrad 335/234 FOREIGN PATENTS OR APPLICATIONS 395,271 12/1965 Switzerland 335/229 Primary Examiner-George Harris Attorney-Albert H. Pendleton, Noel I. Smith and P. Phillips Connor et a1.

[5 7] ABSTRACT A bistable electromagnetic actuator has an armature maintained in one stable position magnetically, by means of a permanent magnet, and in a second stable position by means of a spring. Either position may be assumed by energization of a coil with current of the appropriate polarity or by application of mechanical force. A magnetic shunt maintains flux through the permanent magnet during energization of the coil.

9 Claims, 1 Drawing Figure 1 BISTABLE ELECTROMAGNETIC ACTUATOR BACKGROUND OF THE INVENTION This invention relates to bistable electromagnetic actuator and generally to any device having a rectilinearly movable member having two stable positions at opposite ends pf its movement.

It is frequently desirable to provide such apparatus for operating valves, circuit breakers, and other control mechanisms, with provision for having the movable member shift from one to another of its stable positions in response to an electrical pulse or the like. It is also desirable to provide such apparatus with means by which it may be mechanically moved from one to another of its stable positions, without a control pulse.

Accordingly, it is a principal object of the present invention to provide such apparatus in which the movable member has two stable states, and may be readily changed from either state to the other either by manually moving the armature, or by providing a short pulse of direct current of appropriate polarity, in which only a relatively low amplitude pulse is required to change between the states in one direction, with a greater amplitude needed to change states in the reverse direction.

Another object of the present invention is to provide such apparatus with means for holding the armature in either of its two stable positions, the armature being held in one of its stable positions by magnetic means.

Another object of the present invention is to provide such apparatus in which the magnetic holding force is generated by a permanent magnet, with means arranged for maintaining a relatively high remanence of the permanent magnet.

A further object of the present invention is to provide such apparatus which is of simple construction and is economical to fabricate.

These and other objects and advantages of the present invention will become manifest by an examination of the accompanying drawings and the following description.

SUMMARY OF THE INVENTION In one embodiment of the present invention there is provided a solenoid having an armature movable between inner and outer positions, a surrounding coaxial coil, and a case of relatively high magnetic permeability surrounding the coil with means at one end of the case for establishing a path for magnetic flux through the armature, a permanent magnet located within the case, aligned with an end of the-armature and adapted for completing a magnetic circuit through the armature and case when the armature is in its inner position, spring means interconnected between the armature and the case to hold the armature in its extended position, and a magnetic circuit in shunt with the magnet for maintaining a relatively high remanence of the magnet.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be madeto the accompanying drawing which is a vertical elevation, partly in cross section of a solenoid incorporating an illustrative embodiment of the present invention.

DESCRIPTION OF THE INVENTION The attitude of the solenoid 9 illustrated in the draw- I ing is immaterial as it operates in an identical fashion however it may be positioned. The solenoid 9 incorporates a circular cylindrical armature 10 formed of material having a relatively high magnetic permeability. The armature 10 is preferably a body of revolution and has a flange 12 of increased cross section at its lower end, as shown in the drawing. The armature 10 is supported for axial movement relative to a case 14. The case is preferably U-shaped as shown, formed by bending a rectangular strip of ferromagnetic material. The width of the strip is preferably approximately the same dimension as the distance between opposite legs of the U-shaped case, so that the interior of the case is approximately square.

The open end of the case 14 is closed by an end wall 16, having a central aperture for receiving the armature 10. A sleeve 18 is disposed within the aperture and is designed to receive the armature 10 in sliding relation. The sleeve 18 has an annular flange portion 20 adjacent the inner surface of the end wall 16, so that the sleeve 18 is retained in position, relative to the end wall 16, and the lower portion 22 of the sleeve 18 is designed to retain the armature 10 in position within the case 14 by bearing on the upper surface of the flange 12, when the armature is extended so that the lower surface of the flange 12 moves to the dashed line 12'. The lower portion of the sleeve 20 is provided with an enlarged cross section so that it holds a coil form 36 in a coaxial relation with the armature. The sleeve 18 fits closely around the armature 10 in order to minimize the air gap therebetween, but not so tight as to prevent free movement of the armature. The armature 10 is preferably coated with a thin layer of chemically inert TEFLON to resist corrosion and ease the sliding action of the armature. The sleeve 18 extends downwardly along the surface of the armature 10 for a distance, to provide a relatively great area of interface between the sleeve 18 and the armature 10, thereby to reduce reluctance therebetween.

The end wall 16 is secured to the case 14 by any suitable means such as by swagging or staking the end wall and the case together. The case 14, the end wall 16, the sleeve 18 and the armature 10 are all formed of material having a relatively high magnetic permeability so that they can form various paths for magnetic flux, as described hereinafter.

At the bottom of the case 14, as shown in the drawing, the permanent magnet 24 is disposed, held in position by being cemented to the case with a thin layer of cement. The magnet is preferably formed from material having a high magnetic remanence such as Alnico V or the like. A pole piece 26 is secured to the top portion of magnet 24. The pole piece 26 has a lower portion 28 of increased cross section adapted to match the cross section of the upper surface of the magnet 24, and an upper portion 30 of reduced cross section. The pole piece 26 is preferably a body of revolution, so that its upper portion 30 has a circular cylindrical surface. Secured within the case 14 and in contact with the case is a shunt plate 32 having a centrally disposed circular aperture. The shunt plate 32 is disposed at a position within the interior of the case 14 opposite the upper portion 30 of the pole piece 26. The coil form 36, formed of low permeability material, separates the shunt plate 32 from the pole piece 26 to form an annular gap. This gap completes a magnetic circuit extending through the pole piece 26, the magnet 24, the lower portion of the case 14 and the shunt plate 32. The diameter of the upper portion 30 of the pole piece 26 is chosen in relation to the inside diameter of the annular shunt plate 32 to give an air gap of the size required to permit a sufficient amount of flux to flow continuously through the magnetic circuit, in order to prevent demagnetization of the magnet 24. A disk 33, formed of low permeability material, separates the lower portion 28 of the pole piece 26 from the shunt plate 32.

A coil 34 is wound on the circular cylindrical form 36, between flanges 35 and 37 which are pressed onto the coil form 36. The flanges 35 and 37, as well as the coil form 36, are formed of low permeability material. The coil 34 and the coil form 36 are held in position by a resilient spring washer 39, interposed between the upper flange 35 of the coil form 36 and the flange 20 of the sleeve 18. The coil form 36 surrounds the lower portion of the sleeve 18, the lower portion of the annature 10, and the upper portion 30 of the pole piece 26. The coil 34 comprises a solenoid coil formed in a conventional manner and terminating in a pair of wires passing out through appropriate apertures in the end wall 16 for connection to an external circuit.

At a position spaced outwardly from the end wall 16, the actuator 10 is provided with an annular groove which accommodates an E-ring 31. A compression spring 38, surrounding the armature 10, is disposed between the E-ring 31 and the end wall 16.

The assembly of all of the members thus far described provides a unit which is axially symmetric, so that orientation of the parts during assembly is not critical.

When the coil 34 is energized by a d.c. current, a magneto-motive force is produced in one direction or the other in the armature 10, in accordance with the polarity of the source connected to the coil 34, and this causes magnetic flux to flow through the various magnetic circuits.

The solenoid is shown in the drawing with the armature 10 in its lowermost stable position. In this position there is formed a flux path extending from the magnet 24, through the entire case 14, the end wall 16, the bearing 18, the armature l and the pole piece 26. As there is no air gap in this path, the path has relatively little reluctance and, accordingly, a large amount of flux flows through this path. This flux holds the armature in its lower position, and any attempt to move the armature 10 upwardly relative to the pole piece 26, as by the spring 38, is resisted by magnetic force.

A second stable position for the armature 10 is with the armature moved upwardly from the position illustrated in the drawing so that the upper surface of the flange l2 abuts the lower edge of the sleeve 22, the lower surface of the flange 12 then being positioned at the dashed line 12'. When the armature is in this position there is a large air gap between the bottom of the armature l0 and the top of the pole piece 26, so that relatively little flux flows through the magnetic path therebetween, and, accordingly, there is little magnetic force attempting to return the armature to the lower position illustrated in the drawing. The spring 38, supplies a sufficiently large force to hold the armature 10 in its upper position against the magnetic force.

The force of the spring 38 is even greater when the armature 10 is in its lower stable position, but the magnetic force maintaining the armature in this position is sufficiently great to overcome the force of the spring.

An aperture 40 is provided in the outer end of the armature 10 to permit a link or coupling to be connected to the armature 10. By means of such link or coupling, the armature 10 may be moved from one position to another manually or by application of a mechanical force overcoming the spring or magnetic forces, as the case may be, after which the armature 10 remains in its new position after the mechanical force is removed.

The coil 34 is also operable to cause the armature 10 to move from one to the other of its stable positions by a pulse of magnetic force. When the armature is in the lower stable position, as illustrated, application of one voltage polarity to the terminals of the coil 34 produces a flux within the armature 10 which flows in the opposite direction as the flux generated by the magnet 24. This flux flows in a path including the armature 10, the end wall 16, the upper portion of the case 14, the shunt plate 32 and the upper portion of the pole piece 26. As the flux is increased, by increasing the current through the coil 34, the magnetic force acting between the flange l2 and the pole piece 26 is reduced below the level of the force applied in the other direction by the spring 38. Accordingly, the spring 38 becomes effective to move the armature upwardly to its upper stable position.

In a configuration of the present invention like that shown in the drawing, in which the armature is designed to have a A inch stroke with the spring urging the armature upwardly from its lower position with a force of 6 pounds, and in which the coil 34 has a resistance of 6.0 ohms and is constructed of 500 turns of number 31 wire, the armature is caused to move to its upper position by a pulse of 250 ma., or by the discharge of a 200 ufd. capacitor charged to l 1 volts.

After the armature is moved to its upper position, deenergization of the coil 34 does not bring about return of the armature 10 to its lower position because of the increased length of the air gap between the pole piece 26 and the armature 10. The magnetic force between these elements is not sufficient to overcome the force of the spring 38, and the armature 10 is thus held in its upper position by the spring 38. The spring force varies linearly with displacement of the armature 10, while the magnetic force varies expotentially with the length of the air gap. 7

When the armature 10 is in its upper stable position, application of a voltage of opposite polarity tends to produce flux flowing through the same path as heretofore described, but in the reverse direction. This flux adds to magnet-produced flux already present across the relatively large air gap between the flange 12 and the pole piece 26. When the current applied to the coil 24 is sufiiciently large, the combined flux across the air gap gives rise to a magnetic force large enough to overcome the force of the spring 38, and returns the armature 10 to its lower stable position, where it is again retained by the magnetic force of the magnet 24. In the configuration of the invention referred to above, a short pulse of approximately 12.5 amps is operative to return the armature to its lower position.

From the foregoing it will be evident to those skilled in the art that the various electrical and mechanical characteristics of the apparatus may be modified as desired by establishing different values for some of the physical constants of the apparatus. For example, if another spring, having a smaller spring constant, is substituted for the spring 38, a greater force is required to move the armature to its upper position and a lower force is required to move it to its lower position. On the contrary, if a spring is chosen with a larger spring constant, the opposite is true. Preferably a relatively stiff spring is employed in order to enable the apparatus to change its state by application of a low energy pulse, especially when resetting to the other stable state is accomplished mechanically.

If the length of the sleeve 18 is increased, to shorten the stroke of the armature 10, and thus to limit the maximum air gap, there is greater residual field across the air gap between the flange 12 and the pole piece 26 when the armature 10 is in its upper position, so that a weaker pulse applied to the coil 34 is effective to move the armature to its inward position. If the stroke is made greater, by raising the level of the bottom 22 of the sleeve 18, the opposite is true. In this event, the upper end of the sleeve should also be extended, relative to the flange 20, in order to avoid reducing the area of interface between the sleeve 18 and the armature 10.

The interface between the flange 12 and the pole piece 26 is shown as a plane in the drawing, but this may be modified if desired. If the interface is made conical, for example, a different current-force characteristic is obtained for the solenoid, as well known to those skilled in the art.

A particular advantage of the apparatus described in the foregoing is the retention of a large magnetic remanence by the magnet 24. The flux produced by the coil 34 does not function to demagnetize the permanent magnet 24 since it is not required to pass through the permanent magnet 24 itself. Thus the flux passing through the magnet 24 is maintained at a high level, to assure high remanence.

It will be appreciated by those skilled in the art that various modifications can be made in the apparatus described. For example, the open sides of the case 14 may be closed with material having a high magnetic permeability, or alternatively the case 14 may be replaced by a hollow cup-shaped body. In the latter case, the case l4, the end wall'16, and the other elements may all be made bodies of revolution.

It will be seen that improvements have been provided which achieve the aforesaid objects of the present invention.

What is claimed is:

l. A solenoid device comprising a case having first and second opposed end walls and side walls extending between said end walls, a permanent magnet element positioned within said case and interconnected at one end with one of said end walls, an armature extending into said case through the other of said end walls and in magnetic circuit with said other of said end walls, said armature being reciprocable axially of said armature toward and away from said magnet element in said case, coil means in said case surrounding the portion of said armature extending within said case, said coil means extending beyond said armature toward said magnet element, a pole piece interconnected with the inward end of said magnet element and extending into said coil in coaxial alignment with said armature, and a shunt member positioned to provide a magnetic flux path from said pole piece to said side walls between said magnet element and said coil with a gap of low magnetic permeability in said path, said armature contacting said pole piece within said coil at the inward end of such reciprocating movement of said armature to pass substantially all of the magnetic flux generated by said coil through the area of contact between said armature and said pole piece; and said pole piece, said case, said armature and said shunt member being formed of material having high magnetic permeability.

2. A solenoid device comprising a case having first and second opposed end walls and side walls extending between said end walls; a permanent magnet element positioned within said case and interconnected at one end with one of said end walls; an armature extending into said case through the other of said end walls and in magnetic circuit with said other of said end walls, said armature being reciprocable axially of said armature toward and away from said magnet element in said case; coil means in said case surrounding the portion of said armature extending within said case; a pole piece having a first portion in contact with the inward end of said magnet element, a second portion of a lesser cross section than said first portion and extending toward said armature, and having an annular shoulder between said first and second portions; a disk of low magnetic permeability material on said shoulder; said coil means including a coil form of low magnetic permeability material which extends circumjacent said second portion of said pole piece; a shunt member contacting said case and circumscribing the portion of said coil form around said second portion and seated against said disk, whereby such portion of said coil form and said disk define a low magnetic permeability gap between said pole piece and said shunt member; said coil means including a pair of end flanges and being positioned with one of said end flanges adjacent said shunt member and the other of said end flanges adjacent to said other of said end walls; and a resilient element confined between said other end flange and said other of said end walls for retaining said coil means, shunt member and disk in their respective assembled positions; and said pole piece, said case, said armature and said shunt member being formed of material having high magnetic penneability.

3. A solenoid device comprising a case having side walls between two opposed ends of such case; a permanent magnet element positioned within said case adjacent one end thereof, said magnet being interconnected at one pole portion with one end of said side walls and having an opposite pole portion exposed within said case; an armature extending into said case through the other end of said case and in magnetic circuit with the respective adjacent end of said side walls, said armature being reciprocable axially of said annature toward and away from said exposed pole portion of said magnet element in said case; coil means in said case surrounding said armature; a pole piece interconnected with said exposed pole portion of said magnet element within said case and extending toward said armature in coaxial alignment with said armature; a shunt member contacting said side walls and extending closely adjacent to said pole piece to provide a magnetic flux path from said pole piece to said side walls between said magnet element and said coil, said shunt member being spaced from said pole piece to provide a gap of low magnetic permeability therebetween in said path; said armature contacting said pole piece at the inward end of such reciprocating movement of said armature to pass substantially all of the magnetic flux generated by said coil through the area of contact between said armature and said pole piece; and said pole piece, said case, said armature and said shunt member being formed of material having high magnetic permeability.

4. A solenoid device as in claim 3 wherein said shunt member is an annular member having a central aperture of a cross section mating with the cross section of the adjacent portion of said pole piece, and said shunt member circumscribing said pole piece, whereby said gap is an annular gap between said pole piece and the surface of said shunt member defining said aperture.

5. Apparatus according to claim 3, including resilient means for urging said armature outwardly relative to said case.

6. Apparatus according to claim 5, including flange means secured to said armature at a location spaced outwardly from said case, and spring means surrounding said armature between said case and said flange means.

7. Apparatus according to claim 2 wherein said other of said end walls has an aperture therein, and a cylindrical sleeve disposed within said aperture and adapted to receive said armature in sliding relationship therewith, said sleeve formed of material having a high magnetic permeability.

8. Apparatus according to claim 7, including a flange projecting outwardly from said sleeve, said flange being adapted to engage the inner surface of said other of said end walls, said resilient element being confined between said flange of said sleeve and said other end flange of said coil means.

9. Apparatus according to claim 8, wherein said armature has a flange portion of enlarged cross section at said inward end, said flange portion adapted to cooperate with the inwardmost end of said sleeve to limit the movement of said armature in an outward direction.

I l I l 

1. A solenoid device comprising a case having first and second opposed end walls and side walls extending between said end walls, a permanent magnet element positioned within said case and interconnected at one end with one of said end walls, an armature extending into said case through the other of said end walls and in magnetic circuit with said other of said end walls, said armature being reciprocable axially of said armature toward and away from said magnet element in said case, coil means in said case surrounding the portion of said armature extending within said case, said coil means extending beyond said armature toward said magnet element, a pole piece interconnected with the inward end of said magnet element and extending into said coil in coaxial alignment with said armature, and a shunt member positioned to provide a magnetic flux path from said pole piece to said side walls betWeen said magnet element and said coil with a gap of low magnetic permeability in said path, said armature contacting said pole piece within said coil at the inward end of such reciprocating movement of said armature to pass substantially all of the magnetic flux generated by said coil through the area of contact between said armature and said pole piece; and said pole piece, said case, said armature and said shunt member being formed of material having high magnetic permeability.
 2. A solenoid device comprising a case having first and second opposed end walls and side walls extending between said end walls; a permanent magnet element positioned within said case and interconnected at one end with one of said end walls; an armature extending into said case through the other of said end walls and in magnetic circuit with said other of said end walls, said armature being reciprocable axially of said armature toward and away from said magnet element in said case; coil means in said case surrounding the portion of said armature extending within said case; a pole piece having a first portion in contact with the inward end of said magnet element, a second portion of a lesser cross section than said first portion and extending toward said armature, and having an annular shoulder between said first and second portions; a disk of low magnetic permeability material on said shoulder; said coil means including a coil form of low magnetic permeability material which extends circumjacent said second portion of said pole piece; a shunt member contacting said case and circumscribing the portion of said coil form around said second portion and seated against said disk, whereby such portion of said coil form and said disk define a low magnetic permeability gap between said pole piece and said shunt member; said coil means including a pair of end flanges and being positioned with one of said end flanges adjacent said shunt member and the other of said end flanges adjacent to said other of said end walls; and a resilient element confined between said other end flange and said other of said end walls for retaining said coil meAns, shunt member and disk in their respective assembled positions; and said pole piece, said case, said armature and said shunt member being formed of material having high magnetic permeability.
 3. A solenoid device comprising a case having side walls between two opposed ends of such case; a permanent magnet element positioned within said case adjacent one end thereof, said magnet being interconnected at one pole portion with one end of said side walls and having an opposite pole portion exposed within said case; an armature extending into said case through the other end of said case and in magnetic circuit with the respective adjacent end of said side walls, said armature being reciprocable axially of said armature toward and away from said exposed pole portion of said magnet element in said case; coil means in said case surrounding said armature; a pole piece interconnected with said exposed pole portion of said magnet element within said case and extending toward said armature in coaxial alignment with said armature; a shunt member contacting said side walls and extending closely adjacent to said pole piece to provide a magnetic flux path from said pole piece to said side walls between said magnet element and said coil, said shunt member being spaced from said pole piece to provide a gap of low magnetic permeability therebetween in said path; said armature contacting said pole piece at the inward end of such reciprocating movement of said armature to pass substantially all of the magnetic flux generated by said coil through the area of contact between said armature and said pole piece; and said pole piece, said case, said armature and said shunt member being formed of material having high magnetic permeability.
 4. A solenoid device as in claim 3 wherein said shunt member is an annular member having a central aperture of a cross section mating with the cross section of the adjacent portion of said pole piece, and said shunt member circumscribing said pole piece, whereby said gap is an annular gap between said pole piece and the surface of said shunt member defining said aperture.
 5. Apparatus according to claim 3, including resilient means for urging said armature outwardly relative to said case.
 6. Apparatus according to claim 5, including flange means secured to said armature at a location spaced outwardly from said case, and spring means surrounding said armature between said case and said flange means.
 7. Apparatus according to claim 2 wherein said other of said end walls has an aperture therein, and a cylindrical sleeve disposed within said aperture and adapted to receive said armature in sliding relationship therewith, said sleeve formed of material having a high magnetic permeability.
 8. Apparatus according to claim 7, including a flange projecting outwardly from said sleeve, said flange being adapted to engage the inner surface of said other of said end walls, said resilient element being confined between said flange of said sleeve and said other end flange of said coil means.
 9. Apparatus according to claim 8, wherein said armature has a flange portion of enlarged cross section at said inward end, said flange portion adapted to cooperate with the inwardmost end of said sleeve to limit the movement of said armature in an outward direction. 